Freeze-thaw indicator apparatus

Abstract

Apparatus in which melting ice is used to activate a dye formation in producing a color indication of thawing.

We claim: 
     
       1. Freeze-thaw indicator apparatus comprising a plurality of frangible microcapsules, individual ones of which enclose water soluble dye formers mixed in dry form and individual others of which enclose colorless water in liquid form, said dye former and water enclosing microcapsules being securedly positioned on a indicia support such that as surrounding temperatures decrease to freeze the water in liquid form, the ice which is produced causes rupture of its own enclosing microcapsule and that of dye former enclosing microcapsules adjacent to it, and such that as surrounding temperatures thereafter increase above freezing, the ice which melts flows through the ruptures in said water enclosing and adjacent dye former enclosing microcapsules to solubilize the dye formers in dry form to provide a colored dye and a visual indication thereof, with selected ones of said water enclosing microcapsules and selected ones of said dye former enclosing microcapsules being predeterminedly positioned proximate each other and sized of predetermined different construction so as to exhibit a predetermined degree of responsiveness to decreases and increases in surrounding temperature in providing said colored dye and said visual indications, and with said selected water enclosing and dye former enclosing frangible microcapsules providing said visual indications on said support representative of the surrounding temperature to which all of said water enclosing and dye former enclosing frangible microcapsules are subjected and the length of time to which all of said frangible microcapsules are kept at said temperature. 
     
     
       2. The apparatus of claim 1 wherein said selected ones of said dye former and water enclosing microcapsules are operative in providing said visual indication when all of said water enclosing and dye former enclosing frangible microcapsules are subjected to a first surrounding temperature, and wherein selected others of said dye former and water enclosing microcapsules are operative in providing said visual indication when all of said water enclosing and dye former enclosing frangible microcapsules are subjected to a second surrounding temperature. 
     
     
       3. The apparatus of claim 1 wherein said second surrounding temperature is higher above the freezing temperature of said water in liquid form than is said first surrounding temperature. 
     
     
       4. The apparatus of claim 1 wherein said second surrounding temperature is lower below the freezing temperature of said water in liquid form than is said first surrounding temperature. 
     
     
       5. The apparatus of claim 1 wherein said selected ones of said dye former and water enclosing microcapsules are operative in providing a visual indication of a given color when all of said water enclosing and dye former enclosing frangible microcapsules are subjected to said first surrounding temperature and wherein said selected others of said dye former and water enclosing microcapsules are operative in providing a visual indication of another color when all of said water enclosing and dye former enclosing frangible microcapsules are subjected to said second surrounding temperature. 
     
     
       6. The apparatus of claim 1 wherein said selected ones of said dye former and water enclosing microcapsules are operative in providing said visual indication when all of said water enclosing and dye former enclosing frangible microcapsules are subjected to a first surrounding temperature range, and wherein selected others of said dye former and water enclosing microcapsules are operative in providing said visual indication when all of said water enclosing and dye former enclosing frangible microcapsules are subjected to a second surrounding temperature range. 
     
     
       7. The apparatus of claim 1 wherein said selected ones of said dye former and water enclosing microcapsules are operative in providing said visual indication when all of said water enclosing and dye former enclosing frangible microcapsules are subjected to a given temperature for a first length of time, and wherein selected others of said dye former and water enclosing microcapsules are operative in providing said visual indication when all of said water enclosing and dye former enclosing frangible microcapsules are subjected to said temperature for a second length of time. 
     
     
       8. The apparatus of claim 7 wherein said second length of time is of greater duration than said first length of time. 
     
     
       9. The apparatus of claim 1 wherein said selected ones of said dye former and water enclosing microcapsules are constructed of a wall composition different from that of the remaining others of said dye former and water enclosing microcapsules. 
     
     
       10. The apparatus of claim 1 wherein said selected ones of said dye former and water enclosing microcapsules are constructed of a wall thickness different from that of the remaining others of said dye former and water enclosing microcapsules. 
     
     
       11. The apparatus of claim 1 wherein said selected ones of said dye former and water enclosing microcapsules are constructed to enclose volumes of air insulation different from volumes of air insulation enclosed by the remaining other of said dye former and water enclosing microcapsules. 
     
     
       12. The apparatus of claim 1 wherein said selected ones of said water enclosing microcapsules are constructed to enclose different volumes of water than are enclosed by the remaining other of said water enclosing microcapsules. 
     
     
       13. The apparatus of claim 1 wherein said dye formers in dry form are solubilized to a given dye condition by the ice which melts and flows through said ruptures, which condition is not reversed by any subsequent decrease in surrounding temperatures. 
     
     
       14. The apparatus of claim 13 wherein said selected ones of said dye former and water enclosing microcapsules are predeterminedly positioned proximate each other in strip format, and wherein said strip is calibrated along a side thereof to indicate the surrounding temperatures to which all of said frangible microcapsules are subjected. 
     
     
       15. The apparatus of claim 13 wherein said selected ones of said dye former and water enclosing microcapsules are predeterminedly positioned proximate each other in strip format, and wherein said strip is calibrated along a side thereof to indicate the lengths of time to which all of said frangible microcapsules are kept at said temperatures.